The additive manufacturing process is widely known as the three-dimensional (“3D”) printing of objects. Numerous methodologies for 3D printing have been described in prior art, the most common of which include solid-laser-sintering (SLS), stereolithography (SLA), and extrusion-based 3D printing or FFF (fused filament fabrication). All of these methods involve the deposition of thin layer of thermoplastic or thermoset materials.
Prototyping is the most common application for additive manufacturing, using materials such as ABS (acrylonitrile butadiene styrene), Nylon (Polyamide), and PLA (polylactic acid). More recently, 3D printing has been utilizing high performance polymers such as PEI, PPSU, PEEK, etc., as well as metals and ceramics with greater mechanical, chemical, thermal and electrical properties.
PAI is a specialty thermosetting polymer that has the highest strength and stiffness of any thermoplastic polymer. PAI is characterized by good wear, low creep, and excellent chemical and heat resistance; it maintains its mechanical properties up to 275° C. Given its exceptional high-temperature performance, PAI is used in extreme environments for aerospace, defense, and other applications.
The main drawback of PAI is the very lengthy post-curing cycle requiring a complex, programmable oven. According to Solvay's Torlon® processing guide, a portion of which is reproduced as Table 1 below, objects or parts (hereinafter simply “objects”) with thicknesses up to and including 7.6 millimeters (mm) require a 17-day cure schedule involving eight temperature cycles. For larger objects up to 15.9 mm thick, a 23-day cure schedule with ten temperature cycles is required. There are no recommended guidelines for objects thicker than 15.9 mm. If a PAI-based object is machined after curing, then it must undergo a re-curing cycle.
TABLE 1Time and Temperature as a functionof Thickness For a PAI-based ObjectMaximum X-DaysCuresectional thicknessatCumulativeTemperatureof object <mm>Temp.Days<° C.>7.611149121911320414218152321624317252108-172607.6 < Xsect ≤ 15.91114912177131911420415218272323102432122491132541023260
FIG. 1 depicts a flow diagram of prior-art additive manufacturing method 100 for producing a polyamide-imide based object.
Per task 101 of method 100, a 3D model of the object is generated. To create a 3D printable model of a new (non-existing) object, a computer aided design (CAD) package is used to create a digital file (mathematical model) of the object. For an existing object (sculpted or otherwise), a 3D scanner or a digital camera with photogrammetry software is typically used. These latter two approaches collect digital data on the shape and appearance of the real object and then use that data to create the digital file of the object in known fashion.
The digital file/mathematical model must be further processed prior to printing the object. In particular, in task 102, “slicing software,” typically executing on a computer physically separate from the 3D printer, is used to “slice” the 3D model into many (typically hundreds or thousands) of horizontal (2D) layers. The slicing software analyzes the 3D model to determine what “G-code” commands (the instruction set used by most 3D printers) can be used to reproduce the model.
The slicing software generates the G-code instructions based on rules determined by parameters/values provided by the operator/designer along with algorithms within the slicing software itself. Parameters such as filament size, extrusion width, speed of the print head, among others are used to develop the G-code instructions. Once the complete instruction set (the build instructions) is generated, it is transmitted to the 3D printer.
In task 103, the 3D printer deposits material (PAI), corresponding to each “slice,” in sequential fashion in accordance with the build instructions (G-code instruction set). Query, in task 104, whether all layers required for building the object have been deposited. If not, processing loops back, via 105, to task 103 wherein a subsequent layer is deposited per the build instructions.
When all layers are deposited the build is complete and, at task 106, the object is cured.
The post-curing process is unique to PAI resins. The resins start at a low molecular weight, which enables the resin to be processed, injection molded, and extruded. After an object is molded but before its cured, it exhibits very poor mechanical, thermal, electrical, and chemical properties due to its short polymer chains. During the post-curing process, the heat supplied to the object causes the end amic acid groups to form imides generating water as a byproduct. This chemical process occurs at the ends of the short chains, chemically bonding them together resulting in chain extension, cross-linking, and branching.
The reaction is limited by the diffusion of water from the object. The thicker the object, the further the water must diffuse and the longer the required post-curing time.
The art would therefore benefit from a way to reduce the manufacturing lead-time of a PAI-based object. The art would also benefit from a way to build much larger PAI-based objects than is currently practicable given the size limitations that arise from the post-curing process.